1. Field of the Invention
The present invention relates to rigid flame resistant polyurethane foams, particularly ASTM E-84 Class 1 rated urethane modified polyisocyanurate foams.
2. Description of the Prior Art
Rigid polyurethane foams are well known and are commonly prepared from organic polyisocyanates and organic polyols together with known blowing agents, surfactants and catalysts for the reaction of --OH and --NCO groups. Such foams are used in construction, refrigeration and insulation applications because they may be prepared in a wide variety of densities and because they are closed cell foams.
A critical factor in large scale commercial acceptance of a foam for the construction industry and related industries is the ASTM E-84 classification of the particular foam. For fire retardant applications, it has been customary to employ halogenated additives and/or halogenated organic polyols. However, several problems result from the substantial amounts of flame retardant which must be used. The most significant of these problems are the reduced dimensional stability and the increased cost of the foam. A strong need for low Smoke and Flamespread polyurethane foams which do not have these disadvantages therefore exists.
In order to improve the ASTM E-84 performance of foams, aromatic polyester polyols have been used in the production of polyurethane foams and urethane modified polyisocyanurate foams. The use of such polyester polyols is described, for example, in U.S. Pat. Nos. 2,246,365 and 4,039,487. U.S. Pat. No. 4,246,365 teaches that the fire resistance of polyisocyanurate foams can be improved by using polyester polyols based on phthalic acid residues. U.S. Pat. No. 4,039,487 teaches a wide variety of aromatic polyester polyols which are said to produce foams with good ASTM E-84 performance. However, the improvement is limited to the entire foam composite (i.e. foam and surface layer) in which the foam has high friability and low density and thickness.
In an article entitled "The Use of a Unique Aromatic Polyester Polyol in Urethane Modified Isocyanurate Foam Systems" (SPI ANTC, pages 348-351, R. J. Wood, 1983), the use of aromatic polyester polyols combined with various polyethers, solubilizers and relatively low viscosity polyisocyanates is described.
The use of aromatic polyester polyols in combination with sucrose or sucrose-amine based polyethers and low viscosity polyisocyanates is disclosed in U.S. Pat. Nos. 4,459,334 and 4,496,625, and in "New Polyols for Urethane Modified Isocyanurate Foams" (Journal of Cellular Plastics, May-June, 1984, K. B. White et al, pages 215-219). Polyester polyols which are based on aromatic acids, diethylene glycol and propylene glycol are known (See e.g., Technical Data Bulletin-Firemaster PHT4-diol.)
Oligoesters are also known in the art and are described, for example in U.S. Pat. Nos. 3,943,164; 4,435,592; 4,452,997; 4,487,853; 4,535,178; 4,560,788 and 4,582,926. However, no specific advantages with respect to flame retardancy are attributed to them in these disclosures.
Polyester polyols which are the reaction products of polyalkylene terephthalate or recycled polyethylene terephthalate (PET) or dimethyl terephthalate (DMT) with various glycols or glycol blends are also known. Such polyols are disclosed in U.S. Pat. Nos. 4,048,104; 4,223,068; 4,100,354; 4,506,090; 4,436,229 and 4,411,949. Systems based on those polyester polyols which are produced by reacting a polyalkylene terephthalate residue (PET) with glycol (U.S. Pat. No. 4,417,001) and transesterified dimethylterephthalate oxidation residue (U.S. Pat. Nos. 4,237,238; 4,394,286 and 3,647,759) are also known. Polyurethane foams prepared using such polyester polyols exhibit lower Flamespread and Smoke generation ratings than corresponding foams prepared without such polyols when evaluated in accordance with ASTM E-84.
Urethane modified polyisocyanurate foams made from polyester-containing polyol blends in which the fire retardance performance is acceptable only at a density of about 2 pounds per cubic foot or below are described in U.S. Pat. Nos. 4,521,611; 4,526,908 and 4,544,679.
Rigid foams made from etherified modified scrap polyalkylene terephthalate polymers are disclosed in U.S. Pat. No. 4,604,410. However, it is clear from the exemplified foams that when tested in accordance with ASTM E-84, the disclosed foams had Flamespread values of greater than 25. That is, the foams did not satisfy the requirements of a Class 1 foam.
The prior art described above indicates that progress in the development of flame retardant polyurethane and urethane modified polyisocyanurate foams has been made. However, the optimal foam systems with respect to processability, physical and insulation properties, thermal and fire performance properties have not yet been found.
The development of polyurethane and urethane modified polyisocyanurate foams which are able to achieve a Class 1 ASTM E-84 rating for fire retardancy and which has a low Smoke generation rating at densities over 2 pounds per cubic foot, with excellent physical and insulation properties and broad latitude as to processability would be a significant advance of the art.